A cartridge munition comprises a cartridge shell and a projectile inserted into it, with the cartridge shell mechanically attached to the projectile. A propulsion chamber is provided at the base of the cartridge shell to receive a propulsive charge that, for example, may be ignited using an igniter cap. After ignition, propulsive gases from the propulsive charge act on the base of the projectile so that, upon release of the mechanical bond between cartridge shell and projectile, the projectile is driven out of the cartridge shell.
Such a cartridge munition is described in Lubbers, U.S. Pat. No. 5,936,189. This cartridge munition is used with rapid-fire weapons of medium caliber (about 40 mm). Many such cartridges are received into a belt that is fed to the rapid-fire weapon. The propulsion chamber in the cartridge shell is sub-divided into a high-pressure chamber into which the propulsive charge is placed and a low-pressure chamber that is connected with the high-pressure chamber via exhaust apertures. The cartridge shell and projectile are mechanically connected via a central threaded connection that is formed as an intended-break point.
When the propulsive charge is ignited pyrotechnically in the high-pressure chamber by means of an igniter cap, the propulsive charge burns, and propulsive gases are created at high pressure that then act on the projectile base in both chambers. This drives the projectile out of the cartridge shell, after the intended-break point between cartridge shell and projectile is broken.
A similar cartridge munition is described in Lubbers, U.S. Pat. No. 4,892,038.
Such cartridge munitions are used in large quantities, and must both be safely stored and safely transported from the manufacturer to the user. Storage and transport are generally performed using larger cases, e.g., metal cases that hold a large quantity of such cartridges.
In spite of the considerable quantity of igniter material for igniter caps and propulsive charge located within a storage or transport container, storage and transport are generally simple. However, a fire in the storage or transport system during which temperatures reach or exceed about 220° C. presents a risk.
At such temperatures, the pyrotechnic igniter charge of the igniter cap can combust spontaneously, igniting in turn the propulsive charge that otherwise would have ignited at a temperature of from about 320° C. to about 400° C. After the propulsive charge ignites, as during regular firing, enough pressure develops in the propulsion chamber to act on the base of the projectile to eventually rupture the mechanical connection between cartridge shell and projectile, causing them to fly apart explosively.
Significant damage may result simply from the quantity of exploded propulsive charges of a large number of cartridges. The cartridge shell and projectile may cause great damage while flying apart, the cartridge shell and projectile acting as quasi projectiles. Any storage or transport containers involved will be destroyed, whereby the separated cartridge shells and projectiles may endanger humans and cause major mechanical damage.
Haeselich, U.S. Pat. No. 7,107,909 describes the use of a fusible material to prevent unwanted ignition of munitions due to, for example, exposure to fire. The technology described in the Haeselich patent provides for adequate containment in a standard cartridge. However, this technology may be limited in a variety of applications requiring higher working pressures, such as high speed, high velocity ammunitions. More specifically, in some instances proper pressure integrity may not be achievable through the use of the geometric means and potential material selections described in the Haeselich patent.